The invention concerns an apparatus and a method for producing lignocellulosic fibrillar material from wood. The apparatus comprises a rotatable grinding wheel (10) having a rotation axis and around the rotation axis a grinding surface capable of separating fibrillar material from wood by grinding effect, and a feeder (18) for feeding raw wood material against the grinding surface during rotation of the grinding wheel (10). According to the invention, the grinding surface of the grinding wheel (10) comprises a surface profile serrated in the direction of the rotation axis, the serration comprising a pattern of surface features having oblique angle with respect to the rotation axis. The invention provides an efficient industrial-scale apparatus and method for producing lignocellulosic fibrillar material with a large proportion of fine particles.